The invention relates to a valve, especially a valve of a sanitary mixing faucet with at least two sealing disks of sintered ceramic which are in contact with one another.
Ceramic sealing disks above for use in sanitary mixing faucets are widely used and are described, for example, in EP-A-43 456. According to this disclosure an aluminum oxide having a 3 to 25 wt.-% zirconium dioxide content is proposed as the material. With the known sealing disks a reduction of the displacement forces was already achieved, and despite an exceedingly low profile bearing of 10 to 40% an adequate sealing action could still be achieved.
U.S. Pat. No. 4,856,758 discloses sealing disk combinations (plates) for fittings. According to one embodiment, one of the plates is to consist of silicon carbide and the other of the two plates of a hard material of different properties. Examples of such sealing disk combinations are silicon carbide/aluminum oxide or silicon carbide/aluminum silicate. If silicon carbide is proposed as the material for the formation of two sealing disks in contact with one another, the silicon carbide is to have different properties. The limited teaching of that patent is based on providing, in the case of the sealing disk of lesser hardness, a less smooth surface having a plurality of microscopic depressions, so that the bearing surface between the two cooperating plates is greatly reduced. The patent is to be understood in the sense of the formation of a low profile bearing percentage. The silicon carbide materials to be used according to the patent are prepared by infiltration of carbon-containing silicon carbide blanks with metallic silicon--so-called reaction-sintered or reaction-bound silicon carbide.
In DE-C-38 29 506 a valve is described in which the movable valve element and the valve seat element consist of different ceramic materials, the combination of oxidic materials with carbide or nitride materials being mentioned. A disclosure of similar content is found in DE-U-87 15 044 which proposes, for the upper valve part of a sanitary fitting with inlet disk and control disk, the material combination of aluminum oxide and silicon carbide. The silicon carbide material herein proposed is a reaction-sintered silicon carbide (SiC-Si), as already discussed in connection with U.S. Pat. No. 4,856,758. The same material is mentioned for valve disks according to EP-A-63 627 and EP-A-63 762. In the two last-named disclosures an Ra value in the range from 0.1 to 0.15 .mu.m is proposed. The disadvantage of the several times proposed reaction-sintered silicon carbide consists, due to its metallic content, in its low resistance to erosion and corrosion. An additional problem of the known sealing disk combinations in sanitary mixing faucets is that they are required to provide not only an extraordinarily good seal but also very low displacement efforts for their operation. In spite of the many proposals made in the above-described state of the art, it has not yet been possible to reduce the displacement efforts in a satisfactory manner without adding grease as an aid in the assembly of the valve between the sealing disks in contact. It has been found, however, that the grease is gradually flushed out and its effect is lost, with the result that the faucet becomes hard to operate. Moreover, there is an additional disadvantage in the additional production step of greasing.